The invention is based on a circuit arrangement for multiple use of a transformer core of the generic type defined in the Preamble to claim 1.
From the DE 36 16 097 A1, a circuit arrangement is known for actuating one or several power field effect transistors in the switching mode with potential separation through a transformer. The transformer has two secondary windings. The first secondary winding is connected to the control electrode of a first driving transistor connected to positive voltage, and the second secondary winding is connected to a second driving transistor connected to negative voltage or ground potential. The two driving transistors are connected to the gate of the power field effect transistor. The primary winding of the transformer can be admitted with currents flowing in opposite direction, depending on whether the power field effect transistor must be switched on or switched off.
This known circuit arrangement has a transformer, to be sure, which has a primary side winding with center tap and two separate windings on the secondary side, wherein a controlled switch in the form of a transistor is provided in each feed line for the two primary windings. However, it only functions as driving circuit for switching a power field effect transistor on and off.
The invention at hand strives for and achieves a multiple use of an existing transformer by supplying a consumer with energy as well as transmitting drive pulses. This is not the case for the known circuit arrangement.
In contrast, the inventive circuit arrangement for multiple use of a transformer core has the advantage of saving a second inductive element. This results in space and cost savings and thus reduces the necessary total expenditure.
According to the invention, this is generally achieved in that a rectifier is connected to a first secondary winding, in particular for forming a switching power supply which is supplied with energy, and that an FET transistor is connected to a second secondary winding, in particular for forming a drive pulse transmission, which is thus supplied with drive pulses, and that the magnetic circuit for the transformer is actuated from the primary side by different poles.
For a particularly useful embodiment of the invention, the pulse duty factor for switching on the controlled switches is selected to be higher than 50% in the feed lines for the primary windings. It is advantageous if the pulse duty factor for switching on is around 80%.
According to an advantageous modification of the invention, which leads in particular to small structural shapes for the components and thus results in a space saving, the clocking is with high frequency, for example with a frequency of several 100 kHz. In this case, it makes sense if respectively one of the controlled switches in the feed lines to the two primary windings is clocked in a suitable manner.
In accordance with a preferred and advantageous embodiment of the invention, the FET transistor is linked to the second secondary winding via the in-series connection of two Z-diodes with connected cathodes.
If the gate source capacity of the FET transistor is too small, a capacitor can be connected in an advantageous modification of the invention between the gate and the source terminal of the FET transistor.
As a result of the advantageous embodiment of the invention, the FET transistor that is connected to the second secondary winding can be electrically floating.
The inventive circuit arrangement is provided for a particularly advantageous use when generating an independent, stabilized supply voltage and to actuate an electrically floating FET transistor, in particular a MOSFET transistor.
In another useful application, the inventive circuit arrangement is used for control devices for high-pressure gas discharge lamps, in particular in motor vehicle headlamps.